An incandescent light bulb is rated at 60 W when the applied voltage is 120 V (a

Question

An incandescent light bulb is rated at 60 W when the applied voltage is 120 V (a) what is the resistance of the bulb when it is operating? 240 (b) A hot tungsten filament in a bulb has a temperature of about 2520°C. Find the ratio of resistances when the filament is hot to when it is cold, a temperature of 20°C. Information about tungsten is in your text. 12.25 (c) what is the resistance of your bulb when it is cold? 19.59 | (This helps explain why bulbs burn out when switched on.) O Same current always O When it is cold -n. (d) when is the current through the bulb larger, When it is hot (e) The diameter of the wire in a filament is about 0.09 mm. How long is the filament in your bulb? 2224 m | X There is a lot of wire to fit inside a lightbulb. The filament is a coil of a coil. To see photos and read more, check INVSEE or wikipedia. Be sure to look for a microscopic image of the filament

Explanation / Answer

Area

A=pi*D2/4 =pi*(0.09*10-3)2/4=6.36*10-9 m2

Resisitivity of Tungsten

p=5.6*10-8 ohm-m

Since Resistance is given by

R=pL/A

=>L=RA/p =240*(6.36*10-9)/(5.6*10-8)

L=27.26 m

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